The present invention relates generally to apparatus and method for extrusion of synthetic polymeric material into filaments and, more particularly, to the filtration of polymeric material in molten form during extrusion.
In the conventional manufacturing of synthetic textile yarn, a polymer, such as polyester, is basically prepared in a molten state and extruded under pressure through one or more spinning units, commonly referred to as "spin packs," each equipped with a spinneret formed with multiple fine openings through which the molten polymer is extruded in elongate continuous filamentary form. Typically, the multiple filaments emitted from the spinneret openings are collected into a bundle, forming a tow, which is subsequently collected in a can or like container.
Regardless of the care taken to ensure the purity and homogeneity of the molten polymeric material delivered to the spinning units, the polymer material nevertheless will often include minute gelled particles of the polymer of unusually high molecular weight as well as other solid contaminants. As such if such contaminants are not removed prior to extrusion through the spinneret, the fine orifices in the spinneret can become clogged, and further, any such contaminants passing through the spinneret can produce weakened locations in the resultant filament. Hence, it is common practice to provide a polymer filter medium within each spinning unit to perform a final filtration step immediately in advance of extrusion through the spinneret.
In conventional spinning units, the extrusion orifices are commonly arranged in a circular or otherwise annular array with the body of the spinning unit being formed with a corresponding annular passageway opening into direct communication with the spinneret orifices. An annular screen is fitted within the downstream end of the passageway to extend upstream into the passageway with the portion of the passage on the upstream side of the screen being filled with sand or a similar filtering material. Thus, the molten polymer entering the annular passageway must follow a torturous path through and about the sand or other filter material to reach the screen at which the polymer flows inwardly through the screen and therefrom to the spinneret. The screen thereby serves not only to assist in filtration of the polymer but also to prevent the filter material from flowing with the polymer into the orifices of the spinneret.
While such polymer filtration arrangements function satisfactorily to substantially remove most contaminants from the molten polymer, the use of sand or a similar filter material as a filtration medium complicates the fabrication of the spin packs as well the periodic cleaning and maintenance thereof. Further, the screens typically used to retain the filter material in place separated from the spinnerets are typically fabricated of two circular pieces of screen affixed along annular abutting edges by an impervious binder clip, which produces the additional disadvantage of creating a stagnant area of polymer in the area surrounding the binder clip. The rate and efficiency of polymer throughput is accordingly affected.